#include <vector>
using namespace std;

class Solution {
 public:
  bool lemonadeChange(vector<int>& bills) {
    int a = 0, b = 0, c = 0;
    for (int i = 0; i <= bills.size() - 1; i++) {
      if (bills[i] == 5) a++;
      if (bills[i] == 10) a--;
      b++;
      if (bills[i] == 20) {
        if (a > 0 && b > 0) {
          a--;
          b--;
          c++;
        } else
          a = a - 3;
      }
      if (a < 0 || b < 0 || c < 0) {
        return false;
        break;
      }
    }
    return true;
  }
};
